The invention is directed to an operating mechanism for circuit breakers hereinafter referred to as (CB's). More particularly, the invention is directed to low voltage molded-case CB's. Each pole of such CB's comprises a moving contact making or breaking the circuit controlled by the CB, in conjunction with a fixed contact. The moving contacts are associated with a mechanism equipped with a control handle for the opening or closing of the contact pairs, the position of said handle indicating the closed or open condition of the CB. The mechanism comprises a tripping lever associated with an automatic tripping system operated when the current flowing in the circuit reaches abnormally heavy amperage, and thus automatically separating the contacts of the CB. On automatic tripping, the control handle usually adopts a "tripped" position, which is situated between its "closed" and "open" positions. It is then necessary to move the control handle towards its "open" position to reset the mechanism, before it is possible to reclose the CB.
For the safety of the user, it is necessary for the contacts of all poles to be effectively open, when the control handle is in its "CB open" position. This is particularly so, if the CB is equipped for locking in the open condition, namely with a device intended to prevent connection of voltage to the circuit controlled by the CB. It is in fact readily understood, that it would be particularly dangerous if it were possible to lock the control handle in its open position, and thus to believe that the circuit is dead, whereas the contacts of the CB have remained closed.
Devices are known which ensure safety in this respect by placing a bolt or stud in the way of an operating part working with the control handle until the contacts are open, this bolt or stud being moved by a moving contact operating part.
Such a device is described, for example, in French Pat. No. 74 07 529 (publication No. 2,262,859). These devices require locking parts and additional linkages between the control handle and moving contacts of the CB. This takes the form as a special arrangement to prevent control handle locking before normal opening of the contacts. One such arrangement, described in French Pat. No. 74 07 529 consists in making the control handle operate the automatic tripping device, which necessitates yet further additional likages, and complicates operation of the mechanism.